PHYLUM ARTHROPODA 



581 



The eyes (a) are large, compound, and raised on movably articu- 

 lated stalks. The antennules («,) and antenme (ff^) are large, the 

 mandibles (md.) have palps 

 {mt), and the exopodite of 

 the second maxilla (mzt) has 

 the ti>rm of a slender filament 

 which acts as a '"cleaning- 

 foot " to keep the cavity of 

 the carapace free from foreign 

 bodies. There are eight thor- 

 acic appendages (/«/), all of 

 them leaf-like, and recalling 

 those of Apus. The first 

 four abdominal appendages 

 (ill — 2^4) are large biramous 

 swimming-feet, like those of 

 Copepods ; the fifth and sixth 

 {!'■'>, 1''-') Eire small and nni- 

 ramous. 



The Syncarida (Anasjiid- 

 iii-c(i) (Fig. 458) are small, 

 shrimp-like, fresh-water Crus- 

 taceans, which, though re- 

 sembling the rest of the 

 Malacostraca (Eumalacos- 

 traca) in the presence of only 

 six segments in the abdomen 

 and the absence of caudal 

 styles, differ from them in 

 the possession of a combina- 

 tion of features which con- 

 nect them more closely with 

 certain fossil forms of Car- 

 boniferous age. Thus there 

 is no carapace, the thoracic 

 appendages are provided with 

 slender respiratory exopo- 

 dites, and bear a double 

 series of epipodites or bran- 

 chiae; there are stalked eyes 

 and a fan-like tail-fin formed 

 of the telson and the ex- 

 panded uropods. 



The Mysidacca (Fig. 459) 

 are small, transparent, shrimp-like forms, mostly from 2—6 mm. 

 in length. They agree with the Crayfish in the general form 

 of the body, in the union of the head and thorax, in the 



VOL. 1 P P 



Fill. 45V.— Webalia geofiroyi, male, o. eye ; 

 r'l, antemiule la^, antenna ; c, head ; hrf. thoracic 

 feet; d, intestine; h. heart; hm, gizzard; mil. 

 mandible ; ml, niandibnlar palp ; mnt. exo- 

 podite of second maxilla ; '/>]— P4, pleopods ; 

 r. rostrum ; s, carapace ; sm, adductor muscle ; 

 t. testis ; /— VIII, thoracic segments. (From 

 Lang's Comparative Anatouui, after Claus.) 



